Project Summary Abstract Neonatal exposure to nicotine and other psychostimulants has a significant impact on the function of reward- seeking centers affecting nicotine consumption and the susceptibility to drug abuse in the adult. Alteration in circuit activation during development triggers the appearance of dopaminergic phenotype in neurons that normally produce different neurotransmitters. The immediate goal of our research is to understand the functional significance of this novel form of nicotine- induced form of neuroplasticity at the level of identified neurons in the adult brain. The hypothesis is that neonatal activation of a neural circuit induced by nicotine exposure leads to transmitter plasticity in neurons in the activated circuit, which leads to corresponding changes in nicotine consumption and other reward seeking- behaviors in the adult. Our goal is to identify the neurons involved in this novel form of plasticity and determine whether newly expressing dopaminergic (TH+) terminals release dopamine in the reward center to activate target neurons of the nucleus accumbens. The long-term goal of this research is to understand how neural network activation can be used to induce neurotransmitter plasticity to enable therapeutic interventions in the addiction-susceptible brain. These studies will provide new insights into the anatomical and functional plasticity of the developing reward center affecting adult drug preference. Transgenic mouse lines and modern technologies, such as Fast-Scan Cyclic Voltammetry and optogenetics, implemented to measure evoked dopamine release and record neuronal activity (via fiber photometry) in selected classes of neurons enable analysis of the functional significance of neurotransmitter plasticity caused by developmental exposure to psychostimulants as well as its role in reprogramming cellular phenotypes and drug preference in vivo. Significantly, this work will identify the cellular and molecular identity and connectivity of reward-mediating neurons that are nicotine-primed during development to be recruited for dopamine expression and release following secondary nicotine exposure in the adult.